1) Field of the Invention
The field of the present invention generally relates to lighting systems and, more particularly, to interior lighting systems used in transit vehicles or conveyances such as buses, lightrail cars, and the like.
2) Background
Transit vehicles and similar conveyances typically rely on fluorescent lighting to provide illumination, in part because of the historical efficiency of such lighting as compared to, e.g., incandescent lighting. However, fluorescent lighting has drawbacks and limitations.
For example, fluorescent lights have a relatively short lifetime and a high current draw as compared to some other types of lighting, and in particular in comparison with light-emitting diodes (LEDs). In a typical setting, the fluorescent lights receive power from the transit vehicle's battery, which is usually 24 volts, the output of which is “chopped” to provide an alternating current source. The nature of fluorescent lights leads to high electro-magnetic fields, making compatibility with other electrical equipment challenging. Fluorescent lights also often have problems with arcing, which in turn can pose fire dangers or else blow out electrical components and/or cause power ripples.
In addition, fluorescent lighting is not very amenable to flexible control, and can be difficult to dim. For example, if the fluorescent lamp filaments get too cool when attempting to dim the lamp, then the lamp may simply go out. If current continues to flow while the electrodes are at an improper temperature, then severe rapid degradation of the filaments is possible.
Recently, attempts have been made to incorporate LED lights into transit vehicles, in order to overcome some of the drawbacks of fluorescent lighting systems and/or to obtain certain other benefits. Some of these attempts have involved retrofitting existing fluorescent lighting fixtures to utilize LEDs. Typically, this type of retrofitting is accomplished by replacing the fluorescent light tube with a tube-shaped LED fixture having a strip of LEDs surrounded by an opaque glass tube, fitting into the electrical pin connectors that formerly supplied power and physical support to the fluorescent light tube. While this technique may allow for the replacement of fluorescent light tubes with LEDs, it still has drawbacks. For example, the light quality of such fixtures may not be ideal. Also, despite attempts to mask them, the LEDs still generally appear as visible point sources, which is undesirable. In addition, the LEDs may generate a large amount of heat and lead to safety issues or significantly reduced life expectancy.
It would therefore be advantageous to provide a lighting system for a transit vehicle or conveyance, which overcomes one or more of the disadvantages or limitations of conventional lighting systems. It would further be advantageous to provide an LED-based lighting unit that may readily serve to retrofit existing fluorescent lighting in transit vehicles, buses and other conveyances. It would further be advantageous to provide a lighting system which is inexpensive, has improved life expectancy and/or reduced power consumption, requires less wiring, is relatively easy to control, and/or has other benefits and advantages not found in conventional transit vehicle lighting systems.